U.S. patent number 5,671,750 [Application Number 08/695,635] was granted by the patent office on 1997-09-30 for peripheral blood-flow condition monitor.
This patent grant is currently assigned to Colin Corporation. Invention is credited to Masayuki Shinoda.
United States Patent |
5,671,750 |
Shinoda |
September 30, 1997 |
Peripheral blood-flow condition monitor
Abstract
An apparatus for monitoring a peripheral blood-flow condition of
a living subject by detecting a peripheral blood-flow resistance of
the subject, including a first and a second pulse-wave sensor which
are adapted to be worn on a first and a second portion of the
subject, respectively, to detect a first and a second pulse wave,
respectively, each of which is produced in synchronism with a
heartbeat of the subject, a phase-difference determining device for
determining a difference of respective phases of the first and
second pulse waves detected by the first and second pulse-wave
sensors, and a peripheral blood-flow resistance determining device
for determining the peripheral blood-flow resistance of the
subject, based on the phase difference determined by the
phase-difference determining device, according to a predetermined
relationship between peripheral blood-flow resistance and phase
difference.
Inventors: |
Shinoda; Masayuki (Tajimi,
JP) |
Assignee: |
Colin Corporation (Komaki,
JP)
|
Family
ID: |
12270578 |
Appl.
No.: |
08/695,635 |
Filed: |
August 12, 1996 |
Foreign Application Priority Data
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Feb 17, 1995 [JP] |
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7-29235 |
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Current U.S.
Class: |
600/495; 600/490;
600/500; 600/504 |
Current CPC
Class: |
A61B
5/02116 (20130101); A61B 5/0225 (20130101); A61B
5/0285 (20130101); A61B 5/02225 (20130101) |
Current International
Class: |
A61B
5/0225 (20060101); A61B 005/00 () |
Field of
Search: |
;128/672,687,690,691,677,680-3,713 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-0 330 463 |
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Aug 1989 |
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EP |
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A-0 487 726 |
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Jun 1992 |
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EP |
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A-0 750 878 |
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Jan 1997 |
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EP |
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A-61-119239 |
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Jun 1986 |
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JP |
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WO-A-96 22050 |
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Jul 1996 |
|
JP |
|
Primary Examiner: Nasser, Jr.; Robert L.
Attorney, Agent or Firm: Oliff & Berridge
Claims
What is claimed is:
1. An apparatus for monitoring a peripheral blood-flow condition of
a living subject by detecting a peripheral blood-flow resistance of
the subject, comprising:
a first and a second pulse-wave sensor which are adapted to be worn
on a first and a second portion of the subject, respectively, to
detect a first and a second pulse wave, respectively, each of which
is produced in synchronism with a heartbeat of the subject;
phase-difference determining means for determining a difference of
respective phases of said first and second pulse waves detected by
said first and second pulse-wave sensors;
peripheral blood-flow resistance determining means for determining
said peripheral blood-flow resistance of the subject, based on the
phase difference determined by said phase-difference determining
means, according to a predetermined relationship between peripheral
blood-flow resistance and phase difference; and
a blood pressure measuring device which measures a blood pressure
of the subject, and wherein said peripheral blood-flow resistance
determining means determines said peripheral blood-flow resistance
of the subject, based on the phase difference determined by said
phase-difference determining means and the blood pressure measured
by said blood pressure measuring device, according to said
predetermined relationship defined by a function of phase
difference and blood pressure as variables.
2. An apparatus according to claim 1, wherein said blood pressure
measuring device comprises an inflatable cuff adapted to be wound
around a body portion of the subject, and measuring means for
measuring said blood pressure of the subject by changing a pressure
of said cuff applied to the body portion of the subject, and
wherein said first pulse-wave sensor comprises said cuff, a
pressure sensor which detects said pressure of the cuff, and a
pulse-wave filter circuit which extracts, as said first pulse wave,
an oscillatory pressure wave including a plurality of pulses
produced in said cuff in synchronism with the heartbeat of the
subject, from the cuff pressure detected by said pressure
sensor.
3. An apparatus according to claim 2, further comprising a
cuff-pressure regulating device which changes said pressure of said
cuff to a predetermined value lower than a diastolic blood pressure
of the subject and holds the cuff pressure at the predetermined
value, and wherein said pulse-wave filter circuit extracts, as said
first pulse wave, a plurality of heartbeat-synchronous pulses
produced in said cuff held at said predetermined value, from the
cuff pressure detected by said pressure sensor.
4. An apparatus according to claim 2, wherein said second
pulse-wave sensor comprises a pressure pulse wave sensor which is
adapted to be pressed against an artery of the subject via a skin
of the subject, said pressure pulse wave sensor detecting, as said
second pulse wave, a pressure pulse wave including a plurality of
pulses produced from the artery of the subject in synchronism with
the heartbeat of the subject.
5. An apparatus according to claim 1, further comprising
index-value determining means for determining an index value
indicative of a characteristic of a waveform of a decreasing
portion of a heartbeat-synchronous pulse of said second pulse wave
detected by said second pulse-wave sensor, wherein said peripheral
blood-flow resistance determining means comprises correcting means
for correcting, based on said index value determined by said
index-value determining means, said peripheral blood-flow
resistance determined based on said phase difference determined by
said phase-difference determining means.
6. An apparatus according to claim 5, wherein said second
pulse-wave sensor comprises a pressure pulse wave sensor which is
adapted to be pressed against an artery of the subject via a skin
of the subject, said pressure pulse wave sensor detecting, as said
second pulse wave, a pressure pulse wave including a plurality of
pulses produced from the artery of the subject in synchronism with
the heartbeat of the subject.
7. An apparatus according to claim 1, further comprising a display
device which displays, along a time axis, a time-wise trend of
respective values of said peripheral blood-flow resistance
determined by said peripheral blood-flow resistance determining
means.
8. An apparatus according to claim 1, wherein said phase-difference
determining means comprises means for determining a phase
difference of each of heartbeat-synchronous pulses of said first
pulse wave and a corresponding one of heartbeat-synchronous pulses
of said second pulse wave, and wherein said peripheral blood-flow
resistance determining means successively determines, according to
said predetermined relationship, a peripheral blood-flow resistance
of the subject, based on the phase difference of said each
heartbeat-synchronous pulse of said first pulse wave and said
corresponding heartbeat-synchronous pulse of said second pulse
wave.
9. An apparatus for monitoring a peripheral blood-flow condition of
a living subject by detecting a peripheral blood-flow resistance of
the subject, comprising:
a first and a second pulse-wave sensor which are adapted to be worn
on a first and a second portion of the subject, respectively, to
detect a first and a second pulse wave, respectively, each of which
is produced in synchronism with a heartbeat of the subject;
phase-difference determining means for determining a difference of
respective phases of said first and second pulse waves detected by
said first and second pulse-wave sensors;
peripheral blood-flow resistance determining means for determining
said peripheral blood-flow resistance of the subject, based on the
phase difference determined by said phase-difference determining
means, according to a predetermined relationship between peripheral
blood-flow resistance and phase difference; and
index-value determining means for determining an index value
indicative of a characteristic of a waveform of a decreasing
portion of a heartbeat-synchronous pulse of said second pulse wave
detected by said second pulse-wave sensor, wherein said peripheral
blood-flow resistance determining means comprises correcting means
for correcting, based on said index value determined by said
index-value determining means, said peripheral blood-flow
resistance determined based on said phase difference determined by
said phase-difference determining means.
10. An apparatus according to claim 9, wherein said second
pulse-wave sensor comprises a pressure pulse wave sensor adapted to
be pressed against an artery of the subject via a skin of the
subject, said pressure pulse wave sensor detecting, as said second
pulse wave, a pressure pulse wave including a plurality of pulses
produced from the artery of the subject in synchronism with the
heartbeat of the subject.
11. An apparatus according to claim 9, further comprising a display
device which displays, along a time axis, a time-wise trend of
respective corrected values of said peripheral blood-flow
resistance which are provided by said correcting means of said
peripheral blood-flow resistance determining means.
12. An apparatus according to claim 9, wherein said
phase-difference determining means comprises means for determining
a phase difference of each of heartbeat-synchronous pulses of said
first pulse wave and a corresponding one of heartbeat-synchronous
pulses of said second pulse wave, and wherein said peripheral
blood-flow resistance determining means comprises means for
determining, according to said predetermined relationship, a
peripheral blood-flow resistance of the subject, based on the phase
difference of said each heartbeat-synchronous pulse of said first
pulse wave and said corresponding heartbeat-synchronous pulse of
said second pulse wave.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monitor which monitors
peripheral blood-flow condition of a living subject by determining
peripheral blood-flow resistance values of the subject.
2. Related Art Statement
A blood pressure (BP) monitor may be used to monitor BP values of a
patient in an operation room or an intensive care unit (ICU). Even
when the BP monitor reads accurate BP values of the patient, it is,
however, not determinable whether the blood appropriately
circulates or flows through the patient. Hence, a medical person
such as a doctor or nurse may need to monitor peripheral blood-flow
condition of the patient by touching a hand or a foot of the
patient and judging whether the peripheral portion or tissue of the
patient has an extremely low temperature.
Meanwhile, it has been proposed to measure BP values of a patient
from each of his or her trunk and periphery portion and display
respective time-wise trends of the two series of BP values, side by
side, along a common time axis, so that a medical worker can
quickly notice a possible significant change of the peripheral
blood-flow condition of the patient. This technique is employed by
a BP monitor disclosed in Japanese Patent Application filed by the
Assignee of the present U.S. application and laid open for
inspection purposes under Publication No. 61(1986)-119239.
The above-identified BP monitor requires the medical person to
compare two curves representing the two time-wise BP trends with
each other and qualitatively judge whether the peripheral
blood-flow condition of the patient has significantly largely
changed. However, only persons who are well familiar with the
monitor device can make accurate judgments. In addition, the prior
BP monitor does not provide any quantitative reading of the
peripheral blood-flow condition of the patient. In particular, in
the case where a patient under general anesthesia is monitored, his
or her peripheral blood-flow condition may largely change due to
the excitation of his or her nervous system, the administration of
BP controlling agents, and/or his or her current body temperature.
Therefore, the reading of quantitative values of the peripheral
blood-flow condition of a patient is very important.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
monitor which monitors, with accuracy, the peripheral blood-flow
condition of a living subject by determining peripheral blood-flow
resistance values of the subject.
The above object has been achieved by the present invention, which
provides an apparatus for monitoring a peripheral blood-flow
condition of a living subject by detecting a peripheral blood-flow
resistance of the subject, comprising a first and a second
pulse-wave sensor which are adapted to be worn on a first and a
second portion of the subject, respectively, to detect a first and
a second pulse wave, respectively, each of which is produced in
synchronism with a heartbeat of the subject, phase-difference
determining means for determining a difference of respective phases
of the first and second pulse waves detected by the first and
second pulse-wave sensors, and peripheral blood-flow resistance
determining means for determining the peripheral blood-flow
resistance of the subject, based on the phase difference determined
by the phase-difference determining means, according to a
predetermined relationship between peripheral blood-flow resistance
and phase difference.
In the peripheral blood-flow condition monitor apparatus in
accordance with the present invention, the peripheral blood-flow
resistance determining means determines the peripheral blood-flow
resistance of the subject, based on the phase difference determined
by the phase-difference determining means, according to a
predetermined relationship between peripheral blood-flow resistance
and phase difference. The relationship may be predetermined based
on experimental data, e.g., peripheral blood-flow resistance values
and phase-difference values obtained from many people. The
peripheral blood-flow resistance well reflects the peripheral
blood-flow condition, such that higher peripheral blood-flow
resistance values indicate worse peripheral blood-flow conditions
and lower resistance values indicate better conditions. Thus, the
present monitor apparatus monitors, with accuracy, the peripheral
blood-flow condition of a living subject by determining the
peripheral blood-flow resistance values of the subject.
According to a preferred feature of the present invention, the
monitor apparatus further comprises a blood pressure measuring
device which measures a blood pressure of the subject, and the
peripheral blood-flow resistance determining means determines the
peripheral blood-flow resistance of the subject, based on the phase
difference determined by the phase-difference determining means and
the blood pressure measured by the blood pressure measuring device,
according to the predetermined relationship defined by a function
of phase difference and blood pressure as variables. Since a
mathematical function of phase difference and blood pressure as
variables is used as the relationship for determining the
peripheral blood-flow resistance values of the subject, the present
monitor apparatus monitors, with higher accuracy, the peripheral
blood-flow condition of the subject.
According to another feature of the present invention, the blood
pressure measuring device comprises an inflatable cuff adapted to
be wound around a body portion of the subject, and measuring means
for measuring the blood pressure of the subject by changing a
pressure of the cuff applied to the body portion of the subject,
and the first pulse-wave sensor comprises the cuff, a pressure
sensor which detects the pressure of the cuff, and a pulse-wave
filter circuit which extracts, as the first pulse wave, an
oscillatory pressure wave including a plurality of pulses produced
in the cuff in synchronism with the heartbeat of the subject, from
the cuff pressure detected by the pressure sensor. Since the cuff
is used as not only a part of the blood pressure measuring means
but also a part of the first pulse-wave sensor, the present monitor
apparatus enjoys a simple construction.
According to another feature of the present invention, the monitor
apparatus further comprises a cuff-pressure regulating device which
increases the pressure of the cuff up to a predetermined value
lower than a diastolic blood pressure of the subject and holds the
cuff pressure at the predetermined value, and wherein the
pulse-wave filter circuit extracts, as the first pulse wave, a
plurality of heartbeat-synchronous pulses produced in the cuff held
at the predetermined value, from the cuff pressure detected by the
pressure sensor.
According to another feature of the present invention, the second
pulse-wave sensor comprises a pressure pulse wave sensor which is
adapted to be pressed against an artery of the subject via a skin
of the subject, the pressure pulse wave sensor detecting, as the
second pulse wave, a pressure pulse wave including a plurality of
pulses produced from the artery of the subject in synchronism with
the heartbeat of the subject. Each of the first and second
pulse-wave sensor may otherwise be selected from the group
consisting of an impedance-pulse-wave sensor which includes
electrodes adapted to be held in contact with the surface of a body
portion of a living subject and detects an impedance pulse wave as
the change of impedance of the body portion; a
supersonic-pulse-wave sensor which is held in contact with the
surface of a body portion of a subject, emits supersonic wave
toward an artery of the body portion via the surface, and detects,
as a supersonic pulse wave, the displacement or vibration of the
wall of the artery; or a photoelectric-pulse-wave sensor which is
adapted to be worn on the surface of a body portion of a subject,
emits light toward the body portion, and detects, as a
photoelectric pulse wave, the light reflected from, or transmitted
through, the body portion of the subject.
According to another feature of the present invention, the monitor
apparatus further comprises index-value determining means for
determining an index value indicative of a characteristic of a
waveform of a decreasing portion of a heartbeat-synchronous pulse
of the second pulse wave detected by the second pulse-wave sensor,
wherein the peripheral blood-flow resistance determining means
comprises correcting means for correcting, based on the index value
determined by the index-value determining means, the peripheral
blood-flow resistance determined based on the phase difference
determined by the phase-difference determining means. Thus, the
present monitor apparatus monitors, with higher accuracy, the
peripheral blood-flow resistance condition of the subject.
According to another feature of the present invention, the monitor
apparatus further comprises a display device which displays, along
a time axis, a time-wise trend of respective values of the
peripheral blood-flow resistance determined by the peripheral
blood-flow resistance determining means. A medical person such as a
doctor or nurse can easily notice a significant change of the
peripheral blood-flow condition of the subject by viewing the
screen image of the display device.
According to another feature of the present invention, the
phase-difference determining means comprises means for determining
a phase difference of each of heartbeat-synchronous pulses of the
first pulse wave and a corresponding one of heartbeat-synchronous
pulses of the second pulse wave, and wherein the peripheral
blood-flow resistance determining means successively determines,
according to the predetermined relationship, a peripheral
blood-flow resistance of the subject, based on the phase difference
of the each heartbeat-synchronous pulse of the first pulse wave and
the corresponding heartbeat-synchronous pulse of the second pulse
wave .
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features, and advantages of the
present invention will better be understood by reading the
following detailed description of the preferred embodiments of the
invention when considered in conjunction with the accompanying
drawings, in which:
FIG. 1 is a diagrammatic view of a blood pressure (BP) monitor
which also functions as a peripheral blood-flow condition monitor
to which the present invention is applied;
FIG. 2 is a graph showing an example of a cuff pulse wave provided
by a pulse-wave filter circuit of the BP monitor of FIG. 1, and an
example of a pressure pulse wave (PPW) detected PPW sensor of the
BP monitor of FIG. 1;
FIG. 3 is a graph showing a relationship determined by a control
device of the BP monitor of FIG. 1;
FIG. 4 is a diagrammatic view for explaining various functions of
the control device of the BP monitor of FIG. 1;
FIG. 5 is a graph showing a predetermined relationship between
phase difference or blood pressure and peripheral blood-flow
resistance, pre-stored in the control device of the BP monitor of
FIG. 1;
FIG. 6 is a graph showing a basic relationship between peripheral
blood-flow resistance and phase difference;
FIG. 7 is a graph showing a relationship between blood pressure and
phase difference;
FIG. 8 is a graph for explaining the definition of an index, %MAP,
indicative of a characteristic of the waveform of a decreasing
portion of each heartbeat-synchronous pulse of PPW detected by the
PPW sensor of the BP monitor of FIG. 1;
FIG. 9 is a graph showing a time-wise trend of peripheral
blood-flow resistance values determined by the BP monitor of FIG.
1;
FIG. 10 is a flow chart representing a main control routine
according to which the BP monitor of FIG. 1 operates; and
FIG. 11 is a flow chart representing a peripheral blood-flow
resistance determining routine as one step of the main routine of
FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 to 11, there will be described a blood
pressure (BP) monitor 8 to which the present invention is applied.
The BP monitor 8 may be used to monitor BP values of a patient who
is undergoing, or has undergone, a surgical operation. The BP
monitor also functions as a peripheral blood-flow condition monitor
as described below.
In FIG. 1, the BP monitor 8 includes an inflatable cuff 10
including a rubber bag and a band-like cloth bag in which the
rubber bag is accommodated. The cuff 10 is wound around, e.g., an
upper arm 12 of a patient. The cuff 10 is connected via piping 20
to a pressure sensor 14, a selector valve 16, and a first air pump
18. The selector valve 16 is selectively placed, under control of
an electronic control device 28, in a first state in which the
valve 16 permits pressurized air to be supplied from the air pump
18 to the cuff 10 to increase quickly the air pressure of the cuff
10 (hereinafter, referred to as the "cuff pressure"), a second
state in which the valve 16 causes the cuff 10 to be deflated
slowly, and a third state in which the valve 16 causes the cuff 10
to be deflated quickly.
The pressure sensor 14 detects the cuff pressure (i.e., the air
pressure of the cuff 10), and generates a pressure signal, SP,
representing the detected cuff pressure. The pressure signal SP is
supplied to each of a static-pressure filter circuit 22 and a
pulse-wave filter circuit 24. The static-pressure filter circuit 22
includes a low-pass filter which extracts, from the pressure signal
SP, a cuff-pressure signal, SK, representative of a static or
direct-current component of the pressure signal SP. The
cuff-pressure signal SK is supplied via a first analog-to-digital
(A/D) converter 26 to the control device 28.
The pulse-wave filter circuit 24 includes a band-pass filter which
extracts, from the pressure signal SP, a pulse-wave signal,
SM.sub.1, representative of an oscillating or alternating-current
component of the pressure signal SP, based on a frequency
characteristic of the signal SM.sub.1. The pulse-wave signal
SM.sub.1 is supplied via a second A/D converter 30 to the control
device 28. The alternating-current component represented by the
pulse-wave signal SM.sub.1 corresponds to an oscillatory pressure
wave, i.e., pulse wave which is produced from a brachial artery
(not shown) of the patient in synchronism with the heartbeat of the
patient and is propagated via skin tissue to the cuff 10. This
pulse wave is referred to as the "cuff pulse wave" to be
distinguished from a "pressure pulse wave" which will be described
later. An example of the cuff pulse wave is shown in an upper
portion of the graph of FIG. 2. In the present embodiment, the cuff
10, the pressure sensor 14, and the pulse-wave filter circuit 24
cooperate with one another to provide a first pulse wave sensor 25
(FIG. 4).
The control device 28 is provided by a microcomputer including a
central processing unit (CPU) 29, a read only memory (ROM) 31, a
random access memory (RAM) 33, and an input and output (I/O) port
(not shown). The CPU 29 processes input signals, including the
signals SK, SM.sub.1, by utilizing the temporary-storage function
of the RAM 33, according to control programs pre-stored in the ROM
31. In addition, the CPU 29 supplies drive signals via the I/O port
to drive circuits (not shown) associated with the selector valve 16
and the air pump 18, respectively. Thus, the CPU 29 controls
respective operations of the valve 16 and the pump 18. For example,
when an oscillometric BP measurement using the cuff 10 is carried
out to calibrate the present BP monitor 8, the CPU 29 controls the
valve 16 and the pump 18 to increase quickly the cuff pressure up
to a predetermined target value and subsequently decrease the cuff
pressure at a low rate of 2 to 3 mmHg/sec. Based on the variation
of the cuff pulse wave represented by the pulse-wave signal
SM.sub.1 provided by the pulse-wave filter circuit 24 during the
low-rate decreasing of the cuff pressure, the CPU 29 determines a
systolic and a diastolic BP value of the patient, according to a
known oscillometric BP measuring method. In addition, the CPU 29
controls a display 32 to display the thus determined BP values.
A pressure-pulse-wave (PPW) detecting probe 34 includes a
container-like sensor housing 36, and a fastening band 40 connected
to the sensor housing 36. With the help of the fastening band 40,
the PPW detecting probe 34 is detachably attached to a wrist 42 of
the same arm 12 of the patient on which the cuff 10 is worn, or the
other arm of the patient, such that an opening of the sensor
housing 36 is opposed to a body surface 38 of the patient. A PPW
sensor 46 is secured via an elastic diaphragm 44 to inner surfaces
of the sensor housing 36 such that the PPW sensor 46 is movable
relative to the housing 36 and is advanceable through the opening
of the housing 36 toward the body surface 38 of the patient. The
sensor housing 36 and the diaphragm 44 cooperate with each other to
define a pressure chamber 48, which is supplied with pressurized
air from a second air pump 50 via a pressure regulator valve 52.
Thus, the PPW sensor 46 is pressed on the body surface 38 with a
pressing force, P.sub.HD, corresponding to the air pressure of the
pressure chamber 48. In the present embodiment, the pressing forces
of the PPW sensor 46 applied to the body surface 38 or the radial
artery 56 are indicated in terms of the pressure values (mmHg) of
the pressure chamber 48. The sensor housing 36, the diaphragm 44,
the pressure chamber 48, the second air pump 50, the pressure
regulator valve 52, etc. cooperate with one another to provide a
pressing device which presses the PPW sensor 46 against the radial
artery 56 via the body surface or skin tissue 38.
The PPW sensor 46 includes a semiconductor chip formed of a
monocrystalline silicon which has a press surface 54, and a number
of pressure-sensing semiconductor elements (not shown) which are
arranged, in the press surface 54, in an array at a regular
interval of distance (about 0.2 mm), such that the array of
pressure-sensing elements extends in the direction of width of the
radial artery 56. When the PPW sensor 46 is pressed against the
radial artery 56 via the body surface 38 of the wrist 42, the PPW
sensor 46 detects an oscillatory pressure wave, i.e., pressure
pulse wave (PPW) which is produced from the radial artery 56 in
synchronism with the heartbeat of the patient and is propagated via
the body surface 38 to the PPW sensor 46. The PPW sensor 46
generates a PPW signal, SM.sub.2, representing the detected PPW,
and supplies the PPW signal SM.sub.2 to the control device 28 via a
third A/D converter 58. An example of the pressure pulse wave (PPW)
detected by the PPW sensor 46 is shown in a lower portion of the
graph of FIG. 2, along the same time axis as that of the cuff pulse
wave detected by the first pulse wave sensor 25 and shown in the
upper portion of the graph. The PPW sensor 46 provides a second
pulse wave sensor.
The CPU 29 of the control device 28 processes the input signals,
including the PPW signal SM.sub.2, by utilizing the
temporary-storage function of the RAM 33, according to the control
programs pre-stored in the ROM 31, and supplies drive signals to
drive circuits (not shown) associated with the second air pump 50
and the pressure regulator valve 52, respectively. Thus, the CPU 29
controls respective operations of the pump 50 and the valve 52 to
regulate the pressure of the pressure chamber 48 applied to the PPW
sensor 46, i.e., the pressing force of the PPW sensor 46 applied to
the radial artery 56 via the body surface or skin tissue 38.
When a continuous BP monitoring operation is carried out, the CPU
29 determines an optimum pressing force, P.sub.HDP, of the PPW
sensor 46 applied to the radial artery 56, based on the PPW
detected by the PPW sensor 46 while the pressure of the pressure
chamber 48 is slowly changed, and controls the pressure regulator
valve 52 to maintain the pressure of the chamber 48 at the
determined optimum pressing force P.sub.HDP. In addition, the CPU
29 determines a relationship between BP values and PPW magnitudes
P.sub.M (i.e., voltage values of the PPW signal SM.sub.2), based on
a systolic and a diastolic BP value, SAP, DAP, measured using the
cuff 10 according the oscillometric BP measuring method, and a
maximum and a minimum magnitude, P.sub.Mmax, P.sub.Mmin, of one
heartbeat-synchronous pulse of the PPW detected by the PPW sensor
46 being pressed on the body surface 38 with the optimum pressing
force P.sub.HDP. According to the thus determined relationship, the
CPU 29 determines a systolic and a diastolic BP value (i.e.,
monitor BP values), MBP.sub.SYS, MBP.sub.DIA, of the patient, based
on a maximum magnitude (i.e., upper-peak magnitude) P.sub.Mmax and
a minimum magnitude (i.e., lower-peak magnitude), P.sub.Mmin, of
each of successive heartbeat-synchronous pulses of the PPW detected
by the PPW sensor 46 being pressed with the optimum pressing force
P.sub.HDP. Subsequently, the CPU 29 controls the display 32 to
successively display, for each heartbeat-synchronous pulse, the
thus determined monitor BP values MBP.sub.SYS, MBP.sub.DIA, in
digits, and continuously display the waveform of the PPW detected
by the PPW sensor 46. This waveform represents the instantaneous
monitor BP values MBP of the patient.
FIG. 3 shows an example of a relationship between BP values
(monitor BP values MBP) and PPW magnitudes, P.sub.M, that is
determined by the CPU 29. This relationship is expressed by the
following linear function (1):
where A is a constant corresponding to the slope of the linear
function (1) and B is a constant corresponding to the intercept of
the axis of ordinate indicative of the monitor BP values MBP.
FIG. 4 illustrates various functions of the electronic control
device 28 of the present BP monitor 8. The static-pressure filter
circuit 22 cooperates with the control device 28 to provide a BP
measuring device 72 which measures, according to the oscillometric
BP measuring method (JIS T 1115; JIS is Japanese Industrial
Standard), a systolic BP value SAP and a diastolic BP value DAP of
a living subject based on the variation of respective amplitudes of
heartbeat-synchronous pulses of the cuff pulse wave detected by the
first pulse wave sensor 25 while the pressure of the cuff 10 is
slowly increased or decreased at the rate of 2 to 3 mmHg/sec. The
cuff pulse wave is represented by the pulse-wave signal SM.sub.1
provided by the pulse-wave filter circuit 24. The PPW sensor 46 is
preferably worn on the wrist of the other arm of the patient
different from the arm 12 on which the cuff 10 is worn, and detects
the PPW produced from the radial artery of the other arm. The PPW
sensor 46 provides a second pulse wave sensor. The control device
28 functions as relationship determining means 74 for determining a
MBP-P.sub.M relationship between monitor BP values MBP and PPW
magnitudes P.sub.M that is expressed by the linear function (1) and
is shown in FIG. 3, based on the PPW detected by the PPW sensor 46
and the BP values measured by the BP measuring device 72. The
control device 28 also functions as monitor-BP-value (MBP)
determining means 76 for successively determining, according to the
MBP-P.sub.M relationship, a monitor BP value MBP of the subject
based on a magnitude of each of heartbeat-synchronous pulses of the
PPW detected by the PPW sensor 46. The selector valve 16 and the
first air pump 18 cooperate with the control device 28 to provide a
cuff-pressure regulating device 78 which regulates the air pressure
of the cuff 10 (i.e., cuff pressure), that is detected by the
pressure sensor 14 when each oscillometric BP measurement using the
cuff 10 is carried out. The cuff-pressure regulating device 78
changes the cuff pressure according to a well-known procedure, so
that the BP measuring device 72 can measure BP values of the
patient using the cuff 10 at a regular interval of time and the
relationship determining means 74 calibrates or updates the
MBP-P.sub.M relationship based on the BP values measured using the
cuff 10. For example, the regulating device 78 increases the cuff
pressure up to a target value, e.g., 180 mmHg, which is higher than
an estimated systolic BP value of the patient and subsequently
decreases the cuff pressure slowly at the rate of 2 to 3 mmHg/sec,
during a measurement period in which BP values of the patient are
determined by the BP measuring device 72 according to a well-known
oscillometric BP determining algorithm. After the BP measuring
operation, the regulating device 78 quickly deflates the cuff 10.
In addition, during a continuous BP monitoring operation, the
regulating device 78 maintains the cuff pressure at a predetermined
hold pressure sufficiently lower than a diastolic BP value DAP of
the patient, so that the first pulse wave sensor 25 detects the
cuff pulse wave (i.e., first pulse wave) from the cuff 10 being
held at the predetermined hold pressure.
Moreover, the control device 28 functions as phase-difference
determining means 80. During a continuous BP monitoring operation
in which monitor BP values MBP of the patient are successively
determined by the MBP determining means 76, the phase-difference
determining means 80 successively determines a phase difference,
D.sub.CP (msec), of each of heartbeat-synchronous pulses of the
cuff pulse wave (first pulse wave) obtained from the cuff 10 being
held at the above-described hold pressure and a corresponding one
of heartbeat-synchronous pulses of the pressure pulse wave (second
pulse wave) detected by the PPW sensor 46 from the radial artery
56. The phase differences D.sub.CP determined by the
phase-difference determining means 80 are shown in the graph of
FIG. 2. The first and second pulse wave sensors 25, 46 are worn on
the different arms of the patient, respectively, or the two
different portions of the same arm 12 of the patient,
respectively.
The control device 28 also functions as peripheral blood-flow
resistance determining means 82 for successively determining a
peripheral blood-flow resistance, R.sub.BF, of the patient, based
on each phase difference determined by the phase-difference
determining means 80, according to a predetermined relationship
between peripheral blood-flow resistance R.sub.BF and phase
difference D.sub.CP. The peripheral blood-flow resistance R.sub.BF
determined by the peripheral blood-flow resistance determining
means 82 is defined as an index, MBF/MAP, where MAP is a mean BP
value (mmHg) of the patient and MBF is a mean blood flow rate
(cm.sup.3 /sec) at a peripheral portion or tissue of the
patient.
In the present embodiment, the peripheral blood-flow resistance
determining means 82 determines the peripheral blood-flow
resistance R.sub.BF based on a phase difference and a BP value of
the patient, according to a function of phase difference D.sub.CP
and blood pressure BP as variables shown in the graph of FIG. 5.
FIG. 6 shows a basic relationship between peripheral blood-flow
resistance R.sub.BF and phase difference D.sub.CP, and FIG. 7 shows
a relationship between blood pressure and phase difference
D.sub.CP. The relationship shown in FIG. 5 is derived from the two
relationships shown in FIGS. 6 and 7.
The control device 28 further functions as index-value determining
means 84 for determining an index value indicative of a
characteristic of the waveform of a decreasing portion of each of
heartbeat-synchronous pulses of the PPW detected by the PPW sensor
46, so that the peripheral blood-flow resistance determining means
82 corrects, based on the index value determined by the index-value
determining means 84, the peripheral blood-flow resistance R.sub.BF
determined based on the phase difference determined by the
phase-difference determining means 80. For example, the index value
determined by the index-value determining means 84 may be a
curvature of the waveform of a specific range of the decreasing
portion of each pulse of the PPW, a time constant of the decreasing
portion, or a value, %MAP. The waveform of the decreasing (or
diastolic-period) portion of each PPW pulse reflects a flexibility
or softness of the radial artery 56. In particular, the index %MAP
is defined as a/b.times.100% as indicated in the graph of FIG. 8,
where b is an amplitude obtained by subtracting a minimum magnitude
corresponding to a diastolic BP value DAP from a maximum magnitude
corresponding to a systolic BP value SAP and a is a height of a
magnitude corresponding to a mean BP value MAP, obtained by
subtracting the minimum magnitude from a magnitude corresponding to
the mean BP value MAP. The systolic, diastolic, and mean BP values
SAP, DAP, MAP are measured by the BP measuring device 72.
Otherwise, the value a may be defined as a height of the center of
gravity of an area defined by the waveform of each pulse of the PPW
and the base line corresponding to the diastolic BP value DAP.
Since peripheral blood-flow resistance may be defined by a function
of index %MAP as a variable, the peripheral blood-flow resistance
determining means 82 may determine, according to that function,
another or second peripheral blood-flow resistance of the subject
based on an index value % MAP determined with respect to each pulse
of the PPW, and may correct, based on each second peripheral
blood-flow resistance, a corresponding first peripheral blood-flow
resistance R.sub.BF determined based on a corresponding phase
difference D.sub.CP. For example, each pair of first and second
peripheral blood-flow resistance values are multiplied by a first
weighed coefficient, .alpha. (0<.alpha.<1), and a second
weighed coefficient, .beta. (0<.beta.<1, .alpha.+.beta.=1),
respectively, to obtain two products the sum of which provides a
corrected peripheral blood-flow resistance R.sub.BF. The control
device 28 functions as R.sub.BF -trend displaying means 86 for
controlling the display 32 to display, along a time axis in a
screen image thereof, a time-wise trend of respective values of
peripheral blood-flow resistance R.sub.BF successively determined
and corrected by the peripheral blood-flow resistance determining
means 82. FIG. 9 shows an example of time-wise trend of the
peripheral blood-flow resistance values R.sub.BF.
Next, there will be described the operation of the BP monitor 8
constructed as described above, by reference to the flow charts of
FIGS. 10 and 11 representing the control programs pre-stored in the
ROM 31.
First, at Step SA1, the CPU 29 of the control device 28 controls
the second air pump 50 and the pressure regulator valve 52 to
increase slowly the pressure of the pressure chamber 48, and
determines, as an optimum pressing force P.sub.HDP, a pressure
P.sub.HD of the chamber 48 when the PPW sensor 46 detects a maximum
pulse having the greatest amplitude of respective amplitudes of all
the pulses detected thereby during the slow increasing of the
pressure of the chamber 48. Subsequently, the CPU 29 maintains or
holds the pressure of the chamber 48 at the thus determined optimum
pressing force P.sub.HDP. Thus, the optimum pressing force
P.sub.HDP is applied to the PPW sensor 46 to press the radial
artery 56 via the body surface 38.
Next, the control of the CPU 29 proceeds with Step SA2 to start
increasing the pressure of the cuff 10 for measuring actual BP
values of the patient. Step SA2 corresponds to the cuff-pressure
regulating device 78. Step SA2 is followed by Step SA3 to carry out
a known oscillometric BP determining algorithm. Specifically
described, the selector valve 16 is switched to the first state and
the first air pump 18 is operated, so the cuff pressure continues
to increase up to a target pressure (e.g., 180 mmHg) higher than an
estimated systolic BP value of the patient. Subsequently, the air
pump 18 is stopped and the selector valve 16 is switched to the
second state, so that the cuff pressure decreases at a
predetermined low rate (e.g., about 3 mmHg/sec). Based on the
variation of respective amplitudes of heartbeat-synchronous pulses
of the cuff-pulse-wave (CPW) signal SM.sub.1 obtained during this
slow decreasing of the cuff pressure, the CPU 29 determines a
systolic, a mean, and a diastolic BP value SAP, MAP, DAP of the
patient according to the oscillometric BP determining algorithm.
More specifically, the CPU 29 determines, as the systolic BP value
SAP, a cuff pressure at the time when the pulse amplitudes
significantly largely increase, determines, as the diastolic BP
value DAP, a cuff pressure at the time when the pulse amplitudes
significantly largely decrease, and determines, as the mean BP
value MAP, a cuff pressure at the time when the pulse amplitudes
become maximum. In addition, the CPU 29 determines a pulse rate of
the patient based on the interval of time between respective upper
peaks of two successive heartbeat-synchronous pulses of the CPW
signal SM.sub.1. The thus measured BP values and pulse rate are
stored in the RAM 33 and displayed by the display device 32. Then,
the selector valve 16 is switched to the third state and then to
the first state, so that the cuff pressure is first quickly
decreased and then is held at a hold pressure which is
pre-determined to be sufficiently lower than the measured diastolic
BP value DAP. Step SA3 corresponds to the BP measuring means
72.
Subsequently, the control of the CPU 29 goes to Step SA4 to
determine a relationship between monitor BP value MBP and magnitude
P.sub.M of pressure pulse wave (i.e., voltage of the
pressure-pulse-wave (PPW) signal SM.sub.2) as shown in FIG. 3. More
specifically, the CPU 29 newly reads in one heartbeat-synchronous
pulse of the PPW signal SM.sub.2 supplied from the PPW sensor 46,
determines a maximum and a minimum magnitude P.sub.Max, P.sub.Min ,
of the one pulse, and determines the previously-indicated linear
function (1) based on the systolic and diastolic BP values SAP, DAP
of the patient measured at Step SA3 and the thus determined maximum
and minimum magnitudes P.sub.Mmax, P.sub.Mmin , of the one pulse of
the PPW signal SM.sub.2. Step SA4 corresponds to the relationship
determining means 74.
After the MBP-P.sub.M relationship shown in FIG. 3 is determined at
Step SA4, the control of the CPU 29 goes to Step S5 to judge
whether the CPU 29 has read in one heartbeat-synchronous pulse of
the PPW signal SM.sub.2 supplied from the PPW sensor 46 being
pressed at the optimum pressing force P.sub.HDP and has read in a
corresponding heartbeat-synchronous pulse of the CPW signal
SM.sub.1 obtained from the cuff 10 being held at the low hold
pressure. If a negative judgment is made at Step SA5, the CPU 29
waits for detecting one pulse of each of the PPW and CPW signals
SM.sub.1, SM.sub.2. Meanwhile, if a positive judgment is made at
Step SA5, the control of the CPU 29 goes to Step SA6 to determine a
maximum (upper-peak) magnitude P.sub.Max and a minimum (lower-peak)
magnitude P.sub.Mmin , of the one pulse of the PPW signal SM.sub.2.
Step SA6 is followed by Step SA7 to determine a systolic and a
diastolic BP value MBP.sub.SYS, MBP.sub.DIA (monitor BP values) of
the patient, based on the maximum and minimum magnitudes
P.sub.Mmax, P.sub.Mmin , of the one pulse of the PPW signal
SM.sub.2 determined at Step SA6, according to the MBP-P.sub.M
relationship determined at Step SA4. The CPU 29 controls the
display device 32 to display, on its image screen, not only the
thus determined monitor BP values MBP but also the waveform of the
one pulse that is continuous with the waveforms of the previous
pulses. Steps SA6 and SA7 correspond to the MBP determining means
76.
Subsequently, the control of the CPU 29 goes to Step SA8, i.e.,
peripheral blood-flow resistance determining routine represented by
the flow chart of FIG. 11. At Step SA8-1, the CPU 29 determines a
phase difference D.sub.CP (msec) of the one pulse of the CPW signal
SM.sub.1 and the corresponding pulse of the PPW signal SM.sub.2,
based on the signals SM1, SM2 read in at Step SA5. For example, the
CPU 29 determines, as the phase difference D.sub.CP, a time
interval between the respective Upper peaks of the one pulse of the
CPW signal SM.sub.1 and the corresponding pulse of the PPW signal
SM.sub.2, as shown in FIG. 2. Step SA8-1 corresponds to the
phase-difference determining means 80.
Step SA8-1 is followed by Step SA8-2 to determine an index value
%MAP indicative of a characteristic of the waveform of a decreasing
portion of the one pulse of the PPW signal SM.sub.2 read in at Step
SA5. The CPU 29 determines, as the index value %MAP, a ratio a/b
(.times.100%) of a height or magnitude a of the center of gravity
of the area of the one pulse to a pulse amplitude b of the one
pulse, as shown in FIG. 8. The height or magnitude a of the center
of gravity of the area of the one pulse substantially corresponds
to the mean BP value MAP of the subject measured at Step SA3. Step
SA8-2 corresponds to the index-value determining means 84. Step
SA8-2 is followed by Step SA8-3 to determine a peripheral
blood-flow resistance R.sub.BF of the patient based on the actual
phase difference D.sub.CP determined at Step SA8-1 and the BP value
of the patient (the monitor or estimated BP value MBP determined at
Step SA7, or the actual BP value AP measured at Step SA3),
according to the relationship, shown in FIG. 5, which is
pre-determined and is pre-stored in the ROM 31. In the case where
the relationship is pre-determined based on systolic blood pressure
values of human beings, the CPU 29 determines the resistance
R.sub.BF based on the monitor systolic BP value MBP.sub.SYS or the
actual systolic BP value SAP; and, in the case where the
relationship is pre-determined based on diastolic blood pressure
values of human beings, the CPU 29 determines the resistance
R.sub.BF based on the monitor diastolic BP value MBP.sub.DIA or the
actual diastolic BP value DAP.
At Step SA8-3, the CPU 29 corrects, based on the index value %MAP
determined at Step SA8-2, the resistance R.sub.BF determined
according to the relationship shown in FIG. 5. The resistance
R.sub.BF that relates to the flexibility or softness of the walls
of arteries of the patient is also a function of index value %MAP
and BP value of the patient. Accordingly, the CPU 29 determines a
second peripheral blood-flow resistance R.sub.BF2 based on the
index value %MAP solely, or the index value %MAP and BP value in
combination. The CPU 29 determines a weighed average of the first
and second resistances R.sub.BF, R.sub.BF2 by multiplying the two
resistances R.sub.BF, R.sub.BF2 by a first and a second weighing
coefficient .alpha., .beta. (0<.alpha., .beta.<1;
.alpha.+.beta.=1), respectively, and summing the thus obtained two
products. Step SA8-3 corresponds to the peripheral blood-flow
resistance determining means 82. However, this correction may be
omitted.
Step SA8-3 is followed by Step SA8-4 to control the display device
32 to display, on the screen thereof, a time-wise trend of the
corrected peripheral blood-flow resistance values R.sub.BF along an
axis indicative of time as shown in FIG. 9. Step SA8-4 corresponds
to the R.sub.BF -trend displaying means.
Step SA8 is followed by Step SA9 to judge whether a predetermined
period (i.e., calibration period) of about 10 to 20 minutes has
elapsed after a BP measurement using the cuff 10 is carried out at
Step SA3 in the current control cycle. If a negative judgment is
made at Step SA9, the CPU 29 repeats Step SA5 and the following
steps including Step SA8, so that a monitor systolic BP value
MBP.sub.SYS and a monitor diastolic BP value MBP.sub.DIA of the
patient are determined for each heartbeat-synchronous pulse of the
PPW signal SM.sub.2 and displayed by the display device 32.
Meanwhile, if a positive judgment is made at Step SA9, the control
of the CPU 29 goes back to Step SA2 and the following steps to
update the MBP-P.sub.M relationship shown in FIG. 3.
As is apparent from the foregoing description, in the present BP
monitor 8, the phase difference D.sub.CP is determined based on the
cuff pulse wave (first pulse wave) detected by the first pulse wave
sensor 25 and the pressure pulse wave (second pulse wave) detected
by the PPW sensor (second pulse wave sensor) 46, at Step SA8-1, and
the peripheral blood-flow resistance R.sub.BF of the patient is
determined based on the phase difference R.sub.BF according to the
relationship shown in FIG. 5, at Step SA8-3. The first and second
pulse wave sensors 25, 46 are worn on different portions of the
patient. A higher resistance R.sub.BF indicates a worse peripheral
blood-flow condition or state of the patient; and a lower
resistance R.sub.BF indicates a better peripheral blood-flow
condition of the patient. Thus, the resistance R.sub.BF well
reflects the peripheral blood-flow condition of the patient. Thus,
the present BP monitor can monitor, with high accuracy, the
peripheral blood-flow condition of the patient.
When the present BP monitor 8 determines a peripheral blood-flow
resistance R.sub.BF of the patient at Step SA8-3, the CPU 29
utilizes the function of phase difference D.sub.CP and BP value as
variables, shown in FIG. 5. That is, the CPU 29 determines,
according to this function, a resistance R.sub.BF of the patient
based on an actual BP value AP measured at Step SA3 or a monitor BP
value MBP determined at Step SA7, in addition to the phase
difference D.sub.CP determined at Step SA8-1. Thus, the BP monitor
8 can determine, with higher accuracy, the peripheral blood-flow
resistance values R.sub.BF of the subject. Resistance R.sub.BF is a
function of not only phase difference D.sub.CP but also BP
value.
In addition, at Step SA8-2, the CPU 29 determines an index value
%MAP indicative of a characteristic of the waveform of a decreasing
portion of each heartbeat-synchronous pulse of the PPW signal
SM.sub.2. At Step SA8-3, the CPU 29 corrects, based on the index
value %MAP, the peripheral blood-flow resistance value R.sub.BF
determined based on the phase difference D.sub.CP and the BP value
of the subject according to the relationship shown in FIG. 5. Thus,
the BP monitor 8 can determine, with still higher accuracy, the
peripheral blood-flow resistance values R.sub.BF of the
subject.
Moreover, at Step SA8-4, the present BP monitor 8 controls the
display device 32 to display a time-wise trend of the peripheral
blood-flow resistance values R.sub.BF of the subject which have
been determined for the respective heartbeat-synchronous pulses of
the CPW or PPW signal SM.sub.1 or SM.sub.2 obtained at Step SA5.
Thus, a medical person such as a doctor or nurse can easily read
the time-wise change of the resistance R.sub.BF of the patient by
just observing the screen image of the display device 32.
The BP monitor 8 measures actual BP values AP of the patient by
using the cuff 10 being worn on the patient, the pressure sensor 14
for detecting the cuff pressure, and the pulse-wave filter circuit
24 for extracting; from the cuff pressure detected by the sensor
14, the cuff pulse wave that is an oscillatory pressure wave
produced in the cuff 10 in synchronism with the heartbeat of the
patient. The cuff 10, the sensor 14, and the filter circuit 24 also
function as the first pulse wave sensor 25 for detecting the cuff
pulse wave as the first one of the two sorts of pulse waves whose
phase difference is utilized to determine the peripheral blood-flow
resistance R.sub.BF of the patient. Thus, no exclusive first pulse
wave sensor is needed for detecting the first pulse wave and
accordingly the BP monitor 8 enjoys a simple construction.
Similarly, the PPW sensor 46 that is pressed against the artery 56
of the patient via the body surface 38 to detect the pressure pulse
wave produced from the artery 56, also functions as the second
pulse wave sensor for detecting the second pulse wave. Thus, no
exclusive second pulse wave sensor is needed for detecting the
second pulse wave and eventually determining the peripheral
blood-flow resistance R.sub.BF of the patient, and accordingly the
BP monitor 8 enjoys a simpler construction.
While the present invention has been described in its preferred
embodiments, the present invention may otherwise be embodied.
For example, although in the illustrated embodiment the CPU 29
determines the peripheral blood-flow resistance R.sub.BF based on
the phase difference D.sub.CP and the actual or monitor BP value AP
or MBP according to the relationship (i.e., function of two
variables D.sub.CP, AP (or MBP) shown in FIG. 5, it is possible to
determine a peripheral blood-flow resistance of a patient based on
a phase difference D.sub.CP according to the relationship (i.e.,
function of phase difference D.sub.CP) shown in FIG. 6. In
addition, the CPU 29 may determine a peripheral blood-flow
resistance based on an actual index value %MAP according to a
function of index value %MAP and BP value AP (or MBP) or a function
of index value %MAP. In the last case, the first pulse wave sensor
25 may be omitted.
In the illustrated embodiment, the first pulse wave sensor 25 is
provided by the cuff 10, the pressure sensor 14, and the pulse-wave
filter circuit 24 all of which are employed for measuring actual BP
values of a patient, and the second pulse wave sensor is provided
by the PPW sensor 46 which is employed for detecting the pressure
pulse wave and continuously monitoring the blood pressure of the
patient. One or each of the first and second pulse wave sensors
employed for determining the phase difference D.sub.CP of the first
and second pulse waves may be provided by an exclusive pulse wave
sensor which is independent of the function of measuring the BP
values of the patient or the function of detecting the pressure
pulse wave of the patient. The exclusive sensor may be, for
example, an impedance-pulse-wave sensor which includes electrodes
adapted to be held in contact with the surface of a body portion of
a patient and detects an impedance pulse wave as the change of
impedance of the body portion; a supersonic-pulse-wave sensor which
is held in contact with the surface of a body portion of a patient,
emits supersonic wave toward an artery of the body portion via the
surface, and detects, as a supersonic pulse wave, the displacement
or vibration of the wall of the artery; or a
photoelectric-pulse-wave sensor which is adapted to be worn on the
surface of a body portion of a patient, emits light toward the body
portion, and detects, as a photoelectric pulse wave, the light
reflected from, or transmitted through, the body portion of the
subject. The photoelectric-pulse-wave sensor may be one which is
employed by a pulse oximeter or a pulse-rate meter.
While in the illustrated embodiment the. CPU 29 determines, as the
phase difference D.sub.CP, the difference of respective times of
detection of respective upper peaks of each CPW pulse and each PPW
possible to den in FIG. 2, it is possible to determine, as the
phase difference D.sub.CP, the difference of respective times of
detection of respective lower peaks of the two sorts of pulse
waves.
Although the BP monitor 8 measures actual BP values of a patient
according to an oscillometric BP measuring method, it is possible
to employ a microphone for detecting Korotkoff sounds produced from
the arteries underlying the cuff 10 and measures actual BP values
of a patient according to a Korotkoff-sound BP measuring method in
which a systolic and/or a diastolic BP value of the patient are/is
determined based on the appearing and/or disappearing of the
Korotkoff sounds detected by the microphone while the cuff pressure
is changed.
It is to be understood that the present invention may be embodied
with other changes, improvements, and modifications that may occur
to those skilled in the art without departing from the spirit and
scope of the invention defined in the appended claims.
* * * * *